Premiering on Fox on September 10, 1993, Chris Carter’s television blurred the lines between sci-fi, drama, mystery, thriller, and horror and quickly rose from cult hit to one of the most influential TV series of all time. The series revolved around FBI special agents Fox Mulder (David Duchovny) and Dana Scully (Gillian Anderson) who investigate the X-files, or unsolved cases involving the paranormal. Mulder is a firm believer, while his more scientifically minded partner is a skeptic, a dynamic that drives each episode’s investigation into the weird.

While there’s an overlying series’ spanning story arc involving extraterrestrials and conspiracies, the monster of the week episodes that made up most of the series was an absolute highlight. Drawing inspiration from older series like Kolchak: The Night Stalker, Night Gallery, and The Twilight Zone, tuning in to watch what weird phenomena Scully and Mulder would discover next was a blast. Sometimes, it was downright creepy. From Satanic witches to monstrous humanoids, there was no aspect of the paranormal left uncovered in the X-files. Even scarier was that the terrifying entities often escaped the episode, leaving them still out there lurking. In celebration of the 25th anniversary of this acclaimed series, we look back at the 10 creepiest monster of the week episodes.

“Humbug” – Season 2, episode 20

This episode feels straight from Tales from the Crypt and earned a nomination for an Edgar Award. Scully and Mulder head to Gibsonton, Florida to investigate a series of attacks on former circus sideshow performers after a death in the community. Twin Peaks regular Michael J. Anderson is the trailer park manager, and Vincent Schiavelli is an alcoholic with a tumor-like conjoined twin named Leonard. The episode plays around with the concept of the Fiji mermaid, but of course, the true killer is something far creepier. And predictable if you’re familiar with Tales from the Crypt. In keeping with the theme, this episode ends on a darkly humorous note.

“The Host” – Season 2, episode 2

If you weren’t already wary of Porta Potties, this episode will ensure you’ll steer clear in the future. This ep’s monster takes the concept of the parasitic flukeworm and turns it into a humanoid monster that lives in the sewer. The monster’s design, pale and slimy with a fluke mouth, is terrifying enough, but the reveal of what its bite can bring is pure icky body horror. One victim complains of a foul taste in his mouth after surviving an attack, but it’s nothing compared to his vomiting up a flukeworm hours later.

“Badlaa” – Season 8, episode 10

The opening scene in this ep has a large businessman dismissing a paraplegic beggar at the Mumbai, India airport, something he almost instantly comes to regret when the beggar violently pulls him out of the bathroom stall a short while later. Cut to the businessman checking into his hotel in Washington D.C., then bleeding out profusely on the hotel bed. The beggar is revealed to be a mystic inspired by stories of revenge-seeking Indian fakirs. This beggar is out for blood, and that he literally hitches a ride inside someone’s body to make his way overseas is chilling.

“War of the Coprophages” – Season 3, episode 12

Look. Cockroaches are scary. So, this episode already had an advantage toward spine-chilling. But then, of course, The X-Files takes it a step further by making these roaches dung eating extraterrestrial robotic probes with a penchant for swarming and killing. As if that’s not bad enough, there’s a skin-crawling scene that sees a roach burrow into an open wound of a teen. He freaks out and tries to cut it out of his skin, resulting in a bloody death. Director Kim Manners also plays a mean trick on the audience by having a roach scurry across the screen, making you question if your own home has been invaded.

“Squeeze” – Season 1, episode 3

The mystery at the heart of this episode sees Scully and Mulder investigate a series of brutal murders that seem to reoccur every 30 years. What they eventually find is Eugene Victor Tooms (Doug Hutchison), a mutant that feeds off human livers before going into hibernation for 30 years. He also has the ability to squeeze into tight places, making him hard to track without obvious points of entry in the victims’ homes. The weird hibernation nests that Tooms makes, bound together by his bile, is icky enough, but it’s Hutchison’s unnerving performance that makes Tooms an all-time creepy villain. The character returns in episode 21.

“Chinga” – Season 5, episode 10

Co-written by Stephen King, Chinga featured Scully on vacation in Maine, only to find herself drawn into the mysterious case of a creepy girl and her creepier doll when she stumbles upon a grocery store full of bloodied victims of self-mutilation. The girl’s mother lives in fear and is plagued with visions of the next victim to fall prey to the girl and her evil doll. Mulder sticks to the sidelines in this ep, leaving Scully to contend with a nightmarish killer doll on her own.

“Sanguinarium” – Season 4, episode 6

The cold open is one gnarly, gruesome foray into plastic surgery gone wrong, instilling or reinforcing the fear of being put under the knife. From there, Scully and Mulder are called in to investigate as the doctor had no recollection of killing his patient. It’s the first of many botched surgeries resulting in horrific deaths, but when Mulder finds pentagrams he suspects witchcraft. Any episode in which The X-files dabbled in black magic, Satanism, and witchcraft (see the next two entries) is a creepy delight, and this gruesome plastic surgery-themed ep is among the best. Slurpy wet sounds and all.

“Die Hand Die Verletzt” – Season 2, episode 14

When teens go into the woods to play with black magic, one doesn’t come back out alive. Enter Scully and Mulder, who find the faculty of the local high school aren’t the conservatives they appear to be, but Satanic worshippers that don’t realize they’re in over their heads. If you’re afraid of snakes, then this episode’s death by snake will deliver nightmare fuel. Even still, it’s nothing compared to the nightmare that is substitute teacher Mrs. Phyllis Paddock (Susan Blommaert).

“Familiar” – Season 11, Episode 8

Two words: Mr. Chuckleteeth. With an opening feeling very familiar to It, right down to a raincoat sporting little boy wandering off alone to his violent demise, Mr. Chuckleteeth instills himself as one of the more terrifying entities of the series. He’s not the only terrifying kid’s show character to terrorize, as a demonic Teletubbies copycat also makes an appearance, but he is the most iconic. Of course, the true villain is an evil force summoned by way of witchcraft, unleashing hellhounds, spirits, and evil that’s not quite quelled by episode end.

“Home” – Season 4, episode 2

A darkly satiric look at the traditional family values of America, Home is easily one of the most twisted hours of television. Opening with the live burying of a newborn baby in the middle of a storm, only for its bloody corpse to be discovered by a group of boys playing baseball, this was the first episode to issue a viewer discretion warning for graphic content for the series. The Peacock family feel related to the pack from The Hills Have Eyes. Scully and Mulder plot to save the mother of the dead baby, believing her to be held captive by the deformed Peacock brothers, but the reveal is much, much worse; the woman is the limbless, deformed Peacock matriarch that prefers to reside under the bed. Once seen, the imagery will never leave your head.